Abstract

Thermoplastic polyurethaneureas (TPU) are a unique class of materials that are used in a broad range of applications due to their tailorable chemistry and morphology that allow engineering materials with targeted properties. The central theme of this dissertation is to develop an understanding on polymer-filler interfacial interactions and related reinforcing mechanism of silica nanoparticles in polyether based TPU/silica nanocomposites. Prior to our investigation on nanocomposite materials, the growth of silica nanoparticles in different solvents was studied by monitoring the temporal changes in tetraethyl orthosilicate concentration and in the average diameter of silica particles during initial hydrolysis of tetraethyl orthosilicate in C1-C4 alcohols. Stable silica sols in iso-propanol, which is a common solvent for studied TPU copolymers, were prepared in a controlled manner. Nanocomposites consisting of TPU and silica nanoparticles of various size (20- 250 nm) and filler loadings (1-40 weight%) were prepared by solution blending and characterized. TPU copolymer was based on a cycloaliphatic diisocyanate and hydroxyl terminated poly(tetramethylene oxide) or poly(ethylene oxide) with number average molecular weight of 2000 g/mol and 2-methyl-1,5-diaminopentane chain extender. Even distribution of silica in copolymer matrices led to higher modulus and tensile strength of the nanocomposites, and elastomeric properties were retained. The improvements in tensile properties of the nanocomposites mainly stemmed from the hydrogen-bonding between silanol groups on the surface of silica nanoparticles and ether linkages of the polyether segments of the copolymers. It was demonstrated that polyether based TPU/silica nanocomposites with a range of mechanical properties can be prepared by a simple technique.